Pyrotechnic compositions for gas generant applications

ABSTRACT

Pyrotechnic compositions which include a fuel material of cobalt III nitrate complex with ammonia or water ligands, a burn rate catalyst of copper bis ethylenediamine dinitrate, and an oxidizer of basic copper nitrate are provided to result in relatively high gas outputs and burn rates. Also provided are corresponding or associated gas generating devices and inflatable vehicle occupant safety restraint systems.

BACKGROUND OF THE INVENTION

[0001] This invention relates generally to pyrotechnic compositions and, more particularly, to pyrotechnic compositions such as used in gas generant applications such as in the inflation of automotive inflatable restraint airbag cushions.

[0002] Pyrotechnic gas generant compositions commonly utilized in the inflation of automotive inflatable restraint airbag cushions have previously most typically employed or been based on sodium azide. Such sodium azide-based compositions, upon initiation, normally produce or form nitrogen gas. While the use of sodium azide and certain other azide-based gas generant materials meets current industry specifications, guidelines and standards, such use may involve or raise potential concerns such as involving the safe and effective handling, supply and disposal of such gas generant materials.

[0003] Certain economic and design considerations have also resulted in a need and desire for alternatives to azide-based pyrotechnics and related gas generants. For example, interest in minimizing or at least reducing the overall space requirements for inflatable restraint systems and particularly the space requirements related to the inflator component in such systems has stimulated a quest for gas generant materials which provide relatively higher gas yields per unit volume as compared to typical or usual azide-based gas generants. Further, automotive and airbag industry competition has generally lead to a desire for gas generant compositions which satisfy one or more conditions such as being composed of or utilizing less costly ingredients or materials and being amenable to processing via more efficient or less costly gas generant processing techniques.

[0004] In view of the above, gas generant compositions for pyrotechnic automotive airbag applications generally preferably have a relatively high burn rate, density, and gas output (e.g., preferably producing at least about 3 moles of gas output per 100 grams of composition) and a relatively low combustion flame temperature (e.g., a combustion flame temperature of less than 2000 K), particulate output, lot to lot variability and cost.

[0005] In general, the burn rate for a gas generant composition can be represented by the equation (1), below:

r_(b)=k(P)^(n)   (1)

[0006] where,

[0007] r_(b)=burn rate (linear)

[0008] k=constant

[0009] P=pressure

[0010] n=pressure exponent, where the pressure exponent is the slope of a linear regression line drawn through a log-log plot of burn rate versus pressure.

[0011] Gas generant compositions for automotive airbag applications generally preferably provide or result in a burn rate in excess of 0.3 ips at 1000 psi, with higher burn rate compositions being generally preferred.

[0012] Unfortunately, the development of new gas generant compositions for pyrotechnic automotive airbag applications oftentimes involves a tradeoff between gas output and burn rate. For example, efforts to compensate for the low burn rate of some previously developed non-azide gas generants has resulted in the use of solvent extrusion processing of such formulations into small perforated grains. Solvent extrusion processing, however, requires a drying step following the extrusion. The application of such a drying step has been shown to produce or introduce an undesired variability in resulting gas generant compositions in the form of differences in density in the extruded perforated grains. Consequently, it has proven difficult to develop alternatives to azide-based pyrotechnics and related gas generants and which alternatives simultaneously satisfy automotive airbag application requirements with respect to burn rate and gas output.

[0013] Thus, there is a need and a demand for pyrotechnic compositions which simultaneously satisfy requirements for gas output and burn rate and which compositions also desirably satisfy other requirements such as related to combustion flame temperature, particulate output, lot to lot variability and cost.

SUMMARY OF THE INVENTION

[0014] A general object of the invention is to provide an improved pyrotechnic composition.

[0015] A more specific objective of the invention is to overcome one or more of the problems described above.

[0016] The general object of the invention can be attained, at least in part, through a pyrotechnic composition which includes

[0017] about 45 to about 90 weight percent cobalt III nitrate complex with ligands selected from the group consisting of ammonia and water;

[0018] about 2 to about 50 weight percent of a copper complex of ethylenediamine dinitrate; and

[0019] about 5 to about 50 weight percent basic copper nitrate.

[0020] The prior art generally fails to provide pyrotechnic compositions, such as for use in the inflation of automotive inflatable restraint airbag cushions, and which compositions simultaneously satisfy requirements for gas output and burn rate and which may also desirably satisfy other requirements such as related to combustion flame temperature, particulate output, lot to lot variability and cost.

[0021] The invention further comprehends a pyrotechnic composition which includes about 45 to about 90 weight percent hexammine cobalt III nitrate; about 2 to about 50 weight percent copper bis ethylenediamine dinitrate; and about 5 to about 50 weight percent basic copper nitrate and wherein the composition provides a burn rate of in excess of 0.35 ips at 1000 psi.

[0022] As used herein, references to a specific composition, component or material as a “fuel” are to be understood to refer to a chemical which generally lacks sufficient oxygen to burn completely to CO₂, H₂O and N₂.

[0023] Correspondingly, references herein to a specific composition, component or material as an “oxidizer” are to be understood to refer to a chemical generally having more than sufficient oxygen to burn completely to CO₂, H₂O and N₂.

[0024] References to a component or material as a “burn rate catalyst” are to be understood to refer to such a component or material, when added or included as a minor ingredient, i.e., typically in an amount of less than 20 weight percent and, more commonly in an amount of less than 10 weight percent, produces or results in a significant effect on the burn rate of the composition in which the burn rate catalyst has been added, where a significant effect on burn rate generally involves an increase in burn rate of at least about 20 percent. It will be understood that such burn rate catalyst materials can and typically do undergo reaction when in normal use in a combustion reaction.

[0025] Unless otherwise specifically noted, percentages when used herein in conjunction with a composition ingredient or component are to be understood to be in terms of weight percent.

[0026] Other objects and advantages will be apparent to those skilled in the art from the following detailed description taken in conjunction with the appended claims and drawing.

BRIEF DESCRIPTION OF THE DRAWING

[0027] The FIGURE is a simplified schematic, partially broken away, view illustrating the deployment of an airbag cushion from an airbag module assembly within a vehicle interior, in accordance with one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention generally provides an improved pyrotechnic composition and, more particularly provides an improved pyrotechnic composition such as for use in the inflation of automotive inflatable restraint airbag cushions and which composition simultaneously satisfies requirements for gas output and burn rate and which may also desirably satisfy other requirements such as related to combustion flame temperature, particulate output, lot to lot variability and cost.

[0029] Pyrotechnic compositions in accordance with the invention generally include a unique combination of a cobalt III nitrate complex with ligands selected from the group consisting of ammonia and water, a copper complex of ethylenediamine dinitrate, and basic copper nitrate. In particular, formulations in accordance with a preferred embodiment of the invention generally include:

[0030] about 45 to about 90 weight percent cobalt III nitrate complex with ligands selected from the group consisting of ammonia and water;

[0031] about 2 to about 50 weight percent of a copper complex of ethylenediamine dinitrate; and

[0032] about 5 to about 50 weight percent basic copper nitrate.

[0033] In accordance with one preferred embodiment of the invention, the cobalt III nitrate complex is the main ingredient in the composition and as such is present in a greater relative amount than all the other ingredients of the composition combined. Those skilled in the art and guided by the teachings herein provided will also appreciate that the cobalt III nitrate complex in the subject compositions generally serves or functions as a fuel, as defined above.

[0034] In accordance with one preferred embodiment of the invention, the cobalt III nitrate complex is a hexadentate cobalt III nitrate complex, preferably a hexadentate neutral cobalt III nitrate complex. Hexammine cobalt III nitrate, pentammineaquo cobalt III nitrate and mixtures thereof are particularly preferred cobalt III nitrate complexes for use in the practice of the invention.

[0035] A preferred copper complex of ethylenediamine dinitrate for use in the practice of the invention is copper bis ethylenediamine dinitrate. Further, as detailed below, such copper complexes of ethylenediamine dinitrate can advantageously serve, function or otherwise operate as burn rate catalysts in the subject pyrotechnic compositions.

[0036] In the pyrotechnic formulations of the invention, basic copper nitrate desirably serves or functions to provide oxygen needed or necessary to or for complete combustion of the copper complex of ethylenediamine dinitrate.

[0037] As detailed below, pyrotechnic compositions in accordance with the invention have advantageously been found to provide or result in a burn rate of in excess of 0.35 ips at 1000 psi and, in accordance with at least certain preferred embodiments, a burn rate of at least about 0.4 ips at 1000 psi.

[0038] While the broader practice of the invention is not necessarily limited by or to specific methods of preparation or processing, the compositions of the invention are desirably amenable to relatively simple processing. For example, the copper complex of ethylenediamine dinitrate of the subject pyrotechnic formulations can be formed, such as by reacting cupric nitrate with ethylenediamine, in situ, such as in a spray-dry mix tank. In accordance with one preferred embodiment of the invention, a pyrotechnic composition in accordance with the invention is formed by:

[0039] combining,

[0040] a. the cobalt III nitrate complex with ligands selected from the group consisting of ammonia and water with,

[0041] b. sufficient cupric nitrate and ethylenediamine to form the copper bis ethylenediamine dinitrate and

[0042] c. the basic copper nitrate

[0043] to form a mixture and

[0044] spray drying the mixture to form a powder form of the pyrotechnic composition.

[0045] The pyrotechnic composition powder can then be appropriately press-formed into a desired form, such as in the form of a tablet or wafer, for example.

[0046] As will be appreciated, pyrotechnic compositions or materials prepared in accordance with the invention can be incorporated, utilized or practiced in conjunction with a variety of different structures, assemblies and systems. As representative, the FIGURE illustrates a vehicle 10 having an interior 12 wherein is positioned an inflatable vehicle occupant safety restraint system, generally designated by the reference numeral 14. As will be appreciated, certain standard elements not necessary for an understanding of the invention may have been omitted or removed from the FIGURE for purposes of facilitating illustration and comprehension.

[0047] The vehicle occupant safety restraint system 14 includes an open-mouthed reaction canister 16 which forms a housing for an inflatable vehicle occupant restraint 20, e.g., an inflatable airbag cushion, and an apparatus, generally designated by the reference numeral 22, for generating or supplying inflation gas for the inflation of an associated occupant restraint. As identified above, such a gas generating device is commonly referred to as an “inflator.”

[0048] The inflator 22 contains a quantity of a pyrotechnic composition or material in accordance with the invention and such as suited, upon ignition, to produce or form a quantity of gas such as to be used in the inflation the inflatable vehicle occupant restraint 20. As will be appreciated, the specific construction of the inflator device does not form a limitation on the broader practice of the invention and such inflator devices can be variously constructed such as is also known in the art.

[0049] In practice, the airbag cushion 20 upon deployment desirably provides for the protection of a vehicle occupant 24 by restraining movement of the occupant in a direction toward the front of the vehicle, i.e., in the direction toward the right as viewed in the FIGURE.

[0050] The present invention is described in further detail in connection with the following examples which illustrate or simulate various aspects involved in the practice of the invention. It is to be understood that all changes that come within the spirit of the invention are desired to be protected and thus the invention is not to be construed as limited by these examples.

EXAMPLES Example 1 and Comparative Examples 1 and 2

[0051] In Example 1, a gas generant pyrotechnic composition in accordance with the invention and shown in TABLE 1 below (component values in terms of “wt %”) was prepared and compared to the gas generant pyrotechnic compositions of Comparative Examples 1 and 2, also shown in TABLE 1, below. TABLE 1 Comparative Comparative Ingredient (wt %) Example 1 Example 1 Example 2 bCN 22.53 22.53 46.62 copper bis 10.00 — — ethylenediamine dinitrate HACN 67.47 73.5 — GN — — 50.38 guar gum — 5.00 — aluminum oxide — — 2.70 silicon dioxide — — 0.30

[0052] The gas generant pyrotechnic composition of each of Example 1 and Comparative Examples 1 and 2 was then tested. The burn rate and density values identified in TABLE 2 below were obtained. In particular, the burn rate data was obtained by first pressing samples of the respective gas generant formulations into the shape or form of a 0.5 inch diameter cylinder using a hydraulic press (12,000 lbs force). Typically enough powder was used to result in a cylinder length of 0.5 inch. The cylinders were then each coated on all surfaces except the top one with a krylon ignition inhibitor to help ensure a linear burn in the test fixture. In each case, the so coated cylinder was placed in a 1-liter closed vessel or bomb capable of being pressurized to several thousand psi with nitrogen and equipped with a pressure transducer for accurate measurement of bomb pressure. A small sample of igniter powder was placed on top of the cylinder and a nichrome wire was passed through the igniter powder and connected to electrodes mounted in the bomb lid. The bomb was then pressurized to the desired pressure and the sample ignited by passing a current through the nichrome wire. Pressure vs. time data was collected as each of the respective samples were burned. Since combustion of each of the samples generated gas, an increase in bomb pressure signaled the start of combustion and a “leveling off” of pressure signaled the end of combustion. The time required for combustion was equal to t₂- t₁ where t₂ is the time at the end of combustion and t₁ is the time at the start of combustion. The sample weight was divided by combustion time to give a burning rate in grams per second. Burning rates were typically measured at four pressures (900, 1350, 2000, and 3000 psi). The log of burn rate vs the log of average pressure was then plotted. From this line the burn rate at any pressure can be calculated using the gas generant composition burn rate equation (1), identified above. In addition, the gas yield and flame temperature for the gas generant pyrotechnic composition of each of Example 1 and Comparative Examples 1 and 2 was calculated/determined and are also shown in TABLE 2. TABLE 2 Comparative Comparative PARAMETER Example 1 Example 1 Example 2 Gas Yield 3.3 3.3 2.9 (moles/100 grams) Flame 1800 1805 1850 Temperature (K) Burn Rate 0.40 0.25 0.4-0.5 (ips @ 1000 psi) Density (g/cc) 1.97 (pressed 1.95 (pressed 1.95 (pressed pellet) pellet) pellet) Particulate low low low Lot to Lot low (spray high low Variability dried/pressed) (extruded)

[0053] Discussion of Results

[0054] As shown by the results in TABLE 2, the gas generant pyrotechnic composition in accordance with the invention (i.e., Example 1) advantageously combined the advantages of the gas generant pyrotechnic compositions of Comparative Examples 1 and 2 without also presenting or realizing the disadvantages normally associated with such compositions and without any appreciable difference in the density of the composition. More specifically, the gas generant pyrotechnic composition in accordance with the invention (e.g., Example 1) provided or resulted in higher a gas yield (consistent with the gas generant pyrotechnic composition of Comparative Example 1) while also providing or resulting in a higher burn rate and low lot to lot variability (consistent with the gas generant pyrotechnic composition of Comparative Example 2). Those skilled in the art and guided by the teachings herein provided will appreciate the significance of the increased burn rate provided or resulting from the gas generant pyrotechnic composition in accordance with the invention (e.g., Example 1) such as compared to the gas generant pyrotechnic composition of Comparative Example 1 and such as for the reasons described above.

[0055] Thus, the invention provides pyrotechnic compositions, such as for use in the inflation of automotive inflatable restraint airbag cushions, and which compositions simultaneously satisfy requirements for gas output (e.g., a gas output of at least about 3.0 moles per 100 grams of composition and, preferably, a gas output of about 3.3 moles or more per 100 grams of composition) and burn rate (e.g., a burn rate of in excess of 0.35 ips at 1000 psi and, preferably, a burn rate of at least about 0.4 ips at 1000 psi) and which compositions may also desirably satisfy other requirements such as related to combustion flame temperature, particulate output, lot to lot variability and cost.

[0056] The invention illustratively disclosed herein suitably may be practiced in the absence of any element, part, step, component, or ingredient which is not specifically disclosed herein.

[0057] While in the foregoing detailed description this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purposes of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention. 

What is claimed is:
 1. A pyrotechnic composition comprising: about 45 to about 90 weight percent cobalt III nitrate complex with ligands selected from the group consisting of ammonia and water; about 2 to about 50 weight percent of a copper complex of ethylenediamine dinitrate; and about 5 to about 50 weight percent basic copper nitrate.
 2. The pyrotechnic composition of claim 1 wherein the copper complex of ethylenediamine dinitrate is copper bis ethylenediamine dinitrate
 3. The pyrotechnic composition of claim 1 wherein the cobalt III nitrate complex is a hexadentate cobalt III nitrate complex.
 4. The pyrotechnic composition of claim 3 wherein the hexadentate cobalt III nitrate complex is a hexadentate neutral cobalt III nitrate complex.
 5. The pyrotechnic composition of claim 1 wherein the cobalt III nitrate complex is selected from the group consisting of hexammine cobalt III nitrate, pentammineaquo cobalt III nitrate and mixtures thereof.
 6. The pyrotechnic composition of claim 1 formed by: combining, a. the cobalt III nitrate complex with ligands selected from the group consisting of ammonia and water with, b. sufficient cupric nitrate and ethylenediamine to form the copper bis ethylenediamine dinitrate and c. the basic copper nitrate to form a mixture and spray drying the mixture to form a powder form of the pyrotechnic composition.
 7. The pyrotechnic composition of claim 6 wherein the powder form of the pyrotechnic composition is press-formed into a desired form.
 8. The pyrotechnic composition of claim 1 wherein the composition provides a burn rate of in excess of 0.35 ips at 1000 psi.
 9. The pyrotechnic composition of claim 1 wherein the composition provides a burn rate of at least about 0.4 ips at 1000 psi.
 10. A gas generating device containing the pyrotechnic composition of claim
 1. 11. An inflatable vehicle occupant safety restraint system comprising: the gas generating device of claim 10 connected in association with an inflatable airbag cushion for inflating the airbag cushion.
 12. A pyrotechnic composition comprising: about 45 to about 90 weight percent hexammine cobalt III nitrate; about 2 to about 50 weight percent copper bis ethylenediamine dinitrate; and about 5 to about 50 weight percent basic copper nitrate and, wherein the composition provides a burn rate of in excess of 0.35 ips at 1000 psi.
 13. The pyrotechnic composition of claim 12 wherein the composition provides a burn rate of at least about 0.4 ips at 1000 psi.
 14. The pyrotechnic composition of claim 12 formed by: combining, a. the hexammine cobalt III nitrate with, b. sufficient cupric nitrate and ethylenediamine to form the copper bis ethylenediamine dinitrate and c. the basic copper nitrate to form a mixture and spray drying the mixture to form a powder form of the pyrotechnic composition.
 15. The pyrotechnic composition of claim 14 wherein the powder form of the pyrotechnic composition is press-formed into a desired form.
 16. A gas generating device containing the pyrotechnic composition of claim
 12. 17. An inflatable vehicle occupant safety restraint system comprising: the gas generating device of claim 16 connected in association with an inflatable airbag cushion for inflating the airbag cushion. 